System and method of regulation



Juiiy 1 31.9330 A. M. RSSMAN 1 915,.34

SYSTEM AND METHOD OF REGULATION Filed Aug. 28, 1930 7 Sheets-Sheet lJERRY 4 19330 A M. RQggWflAN L9M3342 SYSTEM AND METHOD OF REGULATIONFiled Aug. 28, 1930 7 Sheets-Sheet 2 INWQE URAFT lg, 2

FORCED DRAFT COAL FEED FIG. 2B

BOILER 3 BOILER 2 A. M. RSSMAN SYSTEM AND METHOD OF REGULATION FiledAug. 28, 1950 '7 Sheets-Sheet 3 y 19330 A. M. RQSSMAN 113716 934- ISYSTEM AND METHOD OF REGULATION Filed Aug. 28, 1930 '7 Sheets-Sheet 4WL/M July 4, 1933. A. M. ROSSMAN SYSTEM AND METHOD OF REGULATION FiledAug. 28, 1930 7 Sheets-Sheet 5 FIG. 5

FIG. 4

A. M. ROSSMAN 1,936,934

SYSTEM AND METHOD OF REGULATION y 1933. A. M. RossMAN 1,916,934

SYSTEM AND METHOD OF REGULATION Filed Aug. 28, 1950 v Sheets-Sheet 7 W 7omm M M m w l vwm ww ALLEN HI. ROSSMAN, OF WILMETTE, ILLINOIS,

OF GHICAGG, ILLINOIEL Patented July 4-, 1933 LUNDY PATENTS CORPORATION,ILLINOIS ASSIG'NOR TO ROSSMAN, SARG-ENT & A. CORPORA'JI'ION OF SYSTEMAND MIETHOD OF REGULATION Application filed August 28, 1930. Serial No.178,521.

T he present invention relates to a method of and means for regulationand is an improwment upon the system and method disclosed in mycopending application, Serial No. 424,380, filed January 29, 1930. Whilethe invention is particularly applicable for combustion control forsteam boilers, and is so shown for illustrative purposes in thisapplication, it is not limited to such use but is of generalapplication.

in controllingcombustion the prime desideratum to maintain a value ofcombustion which is proportional to the steam or other load to becarried. The next desideratuin is to do this efliciently.

AS atmospheric air is substantially constant in composition and as it isthe aim to maintain the efliciency of the furnace and boilersubstantially constant, the amount of air re quired to develop thenecessary heat for carrying the load is substantially directlyproportional to the load. The fuelsuch as wdered coal in this instancema-y then be ed at a rate which will secure substantially complete andeflicient union with the oxygen of the ar supplied to the furnace.

The efliciency of combustion may be check-ed either automatically ormanually, by :1 CO meter or, after calibration of the ins allation, by asteam flow-air flow meter. A team flow-air flow meter is more convenientand prompt in operation than a C0 meter and I show the same as asuitable element for checking th efiiciency of combustion and i. airingadjustment of the controls accordingly, but it is to be understood thatany suitable means which will determine the eiliciency of combustion maybe employed instead.

'llhe air flow through the furnace is maintained by one or more forceddraft fans and one or more induced draft fans. The ei'ficientutilization of the air for supporting the combustion of the fueldepends, amongst other things, upon the ratio of the induced draft to '3a forced draft. if the induced draft is increased it will tend todecrease the pressure within the furnace while if the forced draft isincreased it will tend to increase the furnace pressure. The furnacepressure is therefore a function of the ratioof the induced draft to theforced draft. Hence by determining the furnace pressure, as by the useof an ordinary furnace pressure gauge or the like, the ratio of theinduced draft to the forced draft may be determined, and by suitableresponsive mechanism automatically maintained as desired.

The furnace and boiler may be calibrated to determine the variousabsolute values of air flow and coal feed to steam flow and a general ormean relation established which will be substantially correct forvarious loads within the range of the unit. The regulating sytcm is thenrequired to provide regulation for deviations from the said meanrelation.

in the preferred embodiment of the present invention, as well as in thesystem of the above recited application, I employ variable speed drivesfor controlling directly the rates of fuel feed and air feed. Thesevariable speed drives may be of any preferred form. They may be of thetype shown in my Patent No. 1,830,485, issued November 3, 1931, which isthe preferred form, or they may be of any of the many known forms of Viard Leonard variable speed control. However. insofar as thepresentinvention is concerned any suitable variable speed control systemmay be used, the invention being not limited to the lVa-rd Leonardsystem. The air feed is divided between forced draft fans and induceddraft fans, each fan driven by a variable speed drive. These variablespeed drives are under rhcostat control and hence regulation and controlare greatly simplified.

Assuming that combustion is proceeding at a fixed rate and the steamdemand is increased, such increased demand Will be reflected in areduction of boiler pressure. I employ the steam pressure gauge as amaster gauge to control inv common the speed of the forced draft fans,the induced draft fans and the coal feeders. In place of the steampressure gauge I may use any other means responsive to the change inload on the boiler.

The controller of my invention proportions the rate of correction to theamount of deviation in a novel and efficient manner which.

at the same time, takes care of the conflicting requirements of thefurnace pressure gauge and the efiiciency meter gauge.

In addition to the steam pressure gauge 'or other master controller,means must be provided for constantly maintaining not only the properamount of air flow in proportion to the load on the boiler but also theratio of the induced to the forced draft. This means must be effectiveindependent of the boiler pressure gauge. This is desirable because themaster controller efl'ects changes according to the aforesaid means orgeneral re lation and the special controls are required to cut in whendeviations from the mean are required for the sake of proper efficiencyor proper coordination of the induced and forced draft fans.

In my above referred to patent the special controls cut in to theexclusion of the master control, that is, they render the master controlineffective while they are functioning to correct a deviation that mayhave occurred. My present system differs from that system in that herethe master control is not rendered ineffective during the functioning ofthe special controls. An arrangement is provided whereby the mastercontrol and the special control effect two parts of a differentialdevice which is actuated responsive to the algebraic sum of the twoeffects. The differential may comprise an ordinary mechanicaldifferential wherein two of the movable members constitute drivers forthe third, means being provided for preventing the transmission of aturning force from one driving member to the other; In the embodiment ofmy invention herein illustrated this is accomplished by actuating eachof the driving members of the differential by means including anirreversible worm gear, whereby the driving member may be driven by theactuating means through the worm gear but it can not drive the actuatingmeans,

'' due to the fact that the worm gear is self locking and can transmitpower in one direction only. The third element of the differential willobviously move at a speed and m a direction which are functions of thespeeds and relative directions of operation of the driving members. Thisthird member of the differential varies a resistance which is connectedto control the speed of the fan motor, although it may be arranged tovary the speed 5? of the motor in any other preferred manner.

Since the response of the air supply means is substantiallyinstantaneous, or relatively prompt as compared to the response of thefuel supply means, the adjustment under the control of tl e efficiencymeter for increasing or decreasing the rate of air supply is made tofollow automatically the rate of fuel supply, and is under the controlof two separate controls. namely, first the master controller, whichregulates the fuel and air supply simultaneously, according to apredetermined ratio, and next, under the control of the efiiciency meteror the like, which adjusts the air supply means independently of themaster controller and simultaneously therewith. In the accompanyingembodiment of my invention the efficiency meter varies the air supply tomaintain the ratio of the fuel to air constant. This meter may bearranged to maintain the proper ratio by varying the fuel supply insteadof the air supply.

As between forced and induced draft a relative adjustment is made, inaddition to the main adjustment of the two fans made by the mastercontroller, by means responsive to the furnace pressure which, actingupon the forced draft fan, adjusts its speed relative to the speed ofthe induced draft fan to maintain the proper pressure in the fire box atall times. This latter adjustment is independent of the'mastercontroller and acts whenever necessary, even though the mastercontroller may also be acting at the same time.

In power plants wherein there is provided r a plurality of furnaces theboilers of which arrangement one of the furnaces is considered as themaster furnace and the others are regulated with respectto it inproportion to the respective ratio of load division between the boilers.It is one of the objects of the presentinvention to provide anarrangement wherein the regulation of the load between the respectiveboilers may take place simultaneously with the regulation of theindividual boilers under the action of the special controls thatmaintain the individual boilers operating at their best efficiencies.

Now, to acquaint those skilled in the art with the manner ofconstructing and operating a system according to my invention, I shalldescribe, in connection with the accompanying drawings, a fewembodiments of my invention.

In the drawings Figure 1 is a diagram of a boiler plant to which mysystem of. regulation may be applied;

Figures 2a and 2?) when placed with Figure 2b to the right of and slihtly below the top of Figure 2a constitute a simplified circuit diagramof the connections for obtaining the desired regulation;

Figure 3 is a longitudinal sectional view of the differential and themechanical driving means therefor;

Figure 4; is a top view of the difieren'tial mechanism and the drivingmeans therefor, said view also illustrating the manner whereby thedifferential drives the rheostat controller Figure 5 is a view of therheostat control mechanism Figure 6 shows a modified form of rheostatControl mechanism;

Figure 7 shows a modified form of dilferential control mechanism whereina single motor is used for regulating the controlling rheostat, saidmotor being controlled by a pair of resistors under the separate controlof two sets of relays;

Figure 8 shows an arrangement wherein the differential control isobtained by counterbalancing electromagnetic forces under the control ofthe various regulating means;

and

Figure 9 is a fragmentary circuit diagram illustrating the connectionsto be incorporated in the circuit of Figure 1 to provide for anautomatic regulation of the load as between a plurality of furnaces.

Referring first to Figure 1, I have shown herein diagrammatically themain operating and control parts for a power generating boiler 1, whichmay be of any suitable type. This boiler 1 is provided with a steampressure gauge 2 of a type suitable to operate the electrical controlshereafter to be described. The fire box 3 is shown in this case as firedwith powdered coal through two sets of non zles, l and 5 respectively,having individual means for supplying powdered coal thereto. While theinvention is herein shown as embodied in a steam generating plantemploying powdered fuel it is to be understood that this is merely byway of illustration and not of limitation.

The furnace 3 is fed with coal and air by duplicate apparatus for each,mainly for the sake of reliability. The nozzles and 5 receive theirmixture of powdered coal and air through a passageway 6 from the coalpulvcrizer 7, this mixture being moved by the exhauster 8 driven by asuitable driving motor 9.

Fuel from a suitable source of supply is delivered by a pair of coalfeeders 101O from the hoppers 13. The feeders 10 are driven by feedermotors 12, the speed of these motors being regulable in order to controlthe rate at which fuel is supplied to the boiler. This motor 12 may be avariable speed motor, for example, a D. C. motor or it may be a variablespeed A. C. drive. Coal may, instead, be supplied by constant speedmotors, in which event the rate of fuel feed can be varied by means ofan adjustable coal gate or valve, a pilotmotor being provided forcontrolling the gate or valve. The pulverizer 7 has a gril'iding mill 1%driven by a variable speed electrical drive 15. The exhauster motor 9may be driven at substantially constant speed although this may be avariable speed motor or drive if desired.

Primary air for carrying the pulverized fuel supplied to the pulverizer7 through the duct 16, this duct leading from the forced draft supplyduct 17 leading from the air heater 18. A controlling damper 19, operated by a pilot motor 20 controls the air supply through the duct 16. Inother words, the damper 19 regulates the primary air supply.

The nozzles l are fed with fuel and primary air by apparatus shown atthe left of Figure 1, which is a duplicate of that shown at the right ofFigure 1 and havi g primed reference numerals applied thereto todesignate like parts.

The main air supply to the furnace 8 is furnished by a pair of forceddraft fans 22 and 22, driven by variable speed drive mechanisms .23,These fans 22 and 22 deliver air through the conduits 24, 24 to the airheater 18, 18, which heated by the exhaust gases after they pass throughthe economizer 2:7.

After the air passes out of the air heater 18 into the conduits 1. 17,the major volume ofthe same is delivered to the furnace 3 through thesecondary air supply d ucts 26, 26'. The main volume of air is suppliedthrough the ducts 26, the air supplied through the ducts 1.6, 16 beinginsufficient to support complete combustion of the fuel and servingrather as a carrier of the fuel to bring it into the furnace 3 where itmixes with the main air supply which is required to support combustion.

' The products of combustion pass up through the tubes 0 e the boiler 1then through the economizer 25 then through the air heater 18 and thenceto the conduit 27 leading to the stack 28. The conduit 27 is dividedinto two channels, 29, 29, leading to the induced draft fans 30, 30,which are driven at any desired speed within limit by the variable speeddriving devices 32, 32 which may be of a character similar to thedevices 23, 23 for driving the forced draft fans.

The pressure of air in the furnace is preferably maintained at apressure slightly below atmospheric, generally in the neighborhood of .1of an inch of water, The pressureprevailing in the furnace 3 isindicated upon the furnace pressure gauge 33. When the ratio of inducedto forced draft is proper the above stated pressure, slightly less thanatmospheric, is maintained within the furnace Obviously, in order tovary the rate of steam delivery by the boiler 1, the amount of heatdeveloped in the furnace must be likewise varied, assuming a constantcondition of efiiciency and the like in the boiler and the furnace. Suchvariation in developed heat means variation of the chemical union offuel and oxygen of the air. In order to maintain eflicient combustion itis necessary that the ratio of fuel to air be maintained at a propervalue. Variation of the heat developed, therefore, must be accomplishedby simultaneous variation of air supply and fuel supply in ordertomaintain the efficiency of combustion which is desired. This problemof varying simultaneously the air and fuel is, in the present instance,complicated by the necessity for maintaining the proper ratio of forcedto induced draft, or vice versa.

The eliiciency of combustion is determined by a carbon dioxide meter,generally termed a CO2 meter; this is indicated at 31 as connected tothe conduit 27, through which the products of combustion flow to thestack.

To obtain the best possible combustion efliciency from the boiler it isnecessary to mix with the fuel as nearly as possible the correct amountof air to provide two atoms of oxygen for each atom of carbon in thefuel, or, by weight, 32 parts of oxygen for each 12 parts of carbon inthe fuel. If too much air is furnished too much heat is wasted up thestack. If too little air is furnished, insufficient oxygen is suppliedand not all the fuel is burned. Air in excess of the amountnecessarymust be supplied to insure that, so far as possible, each part of carboncomes in contact with the required two parts of oxygen. To maintaincomplete combustion it has been found that the amount of air suppliedshould be about twice the minimum amount necessary for completecombustion if all of the oxygen were to be consumed. This means thatabout 64 parts of oxygen, by weight, must be supplied for each 12 partsof carbon in the fuel burned. To maintain this ratio about 320 pounds ofair must be furnished for each 12 pounds of carbon in the coal, or about24 to times as much air as carbon in the coal consumed. This ratio ischecked by measuring the percentage of CO in the flue gases, thispercentage being maintained in the neighborhood of 12% to 14% under thebest practicable conditions.

' Instead of employing the CO: meter 31 as means responsive toefficiency of combustion, I may employ a meter 34 which is responsive tothe ratio between steam flow and air flow.

Such steam flow to air flow meters or responsive devices are known andthe construction of the same forms no part of the present invention.Sufice it to say that the flow of air through the furnace may bedetermined by measuring the drop in pressure of the gases passingthrough a portion of the furnace or connections and the flow of steamdelivered may be measured by means of a Pitot tube or the like, and thetwo measurements compared in the meter 3-1 which then responds to theratio of steam flow to air flow which, for a given fuel, should remainsubstantially constant, since a predetermined amount of air is requiredto develop a predetermined amount of steam at constant pressure.

With the boiler in continuous operation and connected to the steam main11, for delivery of steam to a turbine or the like, the load may beassumed to be properly carried, solong as thesteam' pressure gauge 2indicates that an adequate pressure is maintained. That is to say, solong as the steam pressure gauge indicates that a constant pressure ismaintained, therate of combustion is proper for the load carried by theboiler.

Any deviation of the ratio of combustion to load will be evidenced byrise or fall of steam pressure, which will at once affect the gaugeQ.Therefore, with a given speed of the induced draft fans and the forceddraft fans for passing a predetermined amount of air through the firebox per unit of time and with a proper setting of the coal feed 10 anddamper 19to supply the necessary fuel for union with a predeterminedvolume of air and the steam pressure gauge indicating the desiredpressure, the boiler may be assumed to be in proper operation, carryingthe load.

While the deviation from normal pressure by the master steamprcssuregauge is a satisfactory load responsive device, a steam flow meter whichis responsive to steam flow may be employed instead, or any otherelement which is responsive substantially to B. t. u. delivered by theboiler. The master pressure gauge is a simple load responsive devicewhich fulfills the requirements of the present regulating system.

If the boiler pressure or the measurement of steanrflow should drop,indicating that the rate of heat development is not as great asrequired, fuel and air feed should be simultaneously increased inproportion to substantially a predetermined ratio of air and fuel. Thisis then to be carried out by the automatic mechanism (liagrammaticallyshown in Figure 2.

If the resultant ratio of air to fuel is not exactly right to secure thedesired percentage of carbon dioxide in the fuel gases as measured bythe meter 31, a correction of the ratio of air to fuel feed must bemade. Also, in increasing the rate of combustion, the induced draft andforced draft must be simultaneously increased in such a manner as tomaintain the furnace pressure at a proper value as determined by thefurnace pressure gauge v Now it can be seen that the automatic controlsystem is called upon to vary at least three things, namely, forceddraft, induced draft and coal feed, while maintaining a predraft fan andthe induced draft fan 30.

Ref rence 11" new be had more particularly to Figure 2 showing thesystem of cont-rol for the coal feed motor, the induced draft fan"rotors, and tl e forced draft fan motors. l riable rheoccarl0, fl, and42 are provided for controlling the speed of the coal feed motors, theinduced draft motors, and the forced draft motors respective ly. Theresistances of "hose rhcostats are varied in a manner to be presentlydescribed and they are electr illy (JOHHQL ed in any preferred form ofcircuits varyina the speed of the motors involved. The coal feeder motorcontrol may be of the type shown in my above referred to Patent No.1,830,485, to which reference may be had for a full description thereof,or they may be of the lVard Leonard control, or any other pre erred formof speed control insofar as this invention is concerned the speed ofthemotors may b var' l in any preferred manner, not no 7 "\Vard l ieonard.I A

The re stance of tie rheostat 40 is varied by a motor in acting throu;;h a worm l6 and a worm .vheel The nu r connected through a variableresistance and either one of two reversing switches 5t) and 51 to anexciter bus 5.2,this has being energized from a constant volt d ctcurrent bus o l throl i variable rhe at fuses 5b,

and a simcb 57. Upon ization of the relays or to c contacts, til 2 motoris rotated in one direction or the other, depeni'ling upon which relaywas cloc l, and is rotated at a speed which is determined by the valueof the resistance and the resistance 535.

A battery bus is 'ated at 3-3, the upper conduc or of bus be 1;:connected to the positive side of a con nt voltage storage battery andthe lower co uhu-i'jor of this bus connected to the negative side oftl'iat battery. This b s is connected tltrroua'h a fuse switch 52 to apair of coni'luctors (it? which supply potential for rent;

nling' the relays 50 and El, as well as other relays of the system, aswill he more fully pointed out as the description proceeds. The bus 3 ato supplies potential through a fuse switch at tea in or controller 68.llll'iisniastQr controller may be of a construction such as shown in l'iguii'e 52, part 3, o the drawiiurs in my above rcferred to patent, orit may be of any other approved construction, this controller includes asteem llrietly stated,

pres gauge instrumentalit v for applying potei il in one or the othcrofthe two outgoirg conductors (S3 and (if) under the control of thisgauge. is long; as the 'were takento prevent this.

steam pressure remains at normal no potential is applied to either f theconductors 68 or (39. Should the steam pressure fall below normal, thusindicating that the load upon the boiler had increased, then negative lis ap ilied by the controll r to the conduraer $38, which is Ellincrease cozuluctor resulting, in a manner to be more fully set forthpresently, in an increase in the speed of operation of the coal feedmotors as well as of tne induced draft and forced draft n10- tors, thuscausing the furnace to increase its output. Should the steam pressure goup, thus indicating that the furnace output was in excess of the demandupon the boilers, then negative potential is applied to the de creaseconductor 69, which effects a slowing down of the coal feed motors, theforced draft motors, and the induced draft motors, all in a manner to bepresently more fully set forth. Such an arrangement might causeconsiderable hunting unless elaborate means 7 The controller 66 ispreferably one of a standard type now on the market and which appliesthe potential to the conductors 68 or 69 as the case may be by meansof'impulses which are of a duration or of a frequency of occurrencewhich is a function not only of the amount of deviation of the steampressure from normal but also a function of the rate at which the steampressure is varying at the moment, the term rate including alsodirection of the same. i

The increase and decrease conductors 68 and 6.) are connected toincrease and decrease control conductors 68c and 690, respectively,through a double pole double throw switch 72. W hen the switch 72 is inits lowered position the system is under control of the mastercontroller 66. When the switch 72 is thrown to its upper position, thesystem may be controlled by means of a hand switch 75 which upon beingdepressed connects the negative battery bus through the conductor 76, tothe increase conductor 680 Whereas the switch 75 is raised it Connectsthe negative battery bus to the decrease conductor 690. The commonfiring control conductors 68c and 690 a connected to the conductors '50and 71 of the boiler l by means of a manually operable double throwswitch 141. When the switch 141 is in engagement with its right handcont-act, control may be exercised by the master controller 66. When theswitch is operated to close its left hand contact then the control takenaway from the master controller 66 and placed in the hands of a pushbutton switch 142. When the push button switch 142 is depressed itplaces negative battery potential upon the decrease conductor T1, iihereas when this switch is elevated it places negative battery potentialupon the increase conductor Before proceeding further with the de switch89.

scription of the control exercised bythe master controller it may bewell to describe the apparatus for varyingthe resistance of therheostats 41 and 42 for controlling the forced draft and the induceddraft. The resistance of the rheostat 41 is varied by means of a movableelement 80 which is driven by either one or both of two motors 81 and 82connected together through a mechanical dili'erential 83. The mechanicalrelationship between the driving element and the driven element withinthe differential 83 may be as shown more particularly in Figure 3 towhich reference will'be had as the description proceeds. For the presentit may sufiice to state that the motors 81 and 82 each driveditterentones of two of the elements of the differential, the third element orthe spider being driven by those two elements at a speed and in adirection which is the algebraic sum of the motions imparted to theelements driven by the motors. This spider member drives the element 80for varying the resistance of the rheostat 41. The motors 81 and 82drive their respective differential elements through self-locking wormgears whereby neither of the motors can transmit a driving force to theother motor. 1

The operation of the motor 81 is controlled by a pair of electromagneticreversing switches 86 and 87, which are adapted to cause the motor tooperate in either direc tion, said switches connecting the motor to theconstant voltage bus 54 through a fused A variable resistance 90 isincluded in the motor circuit whereby the speed of the motor maybealtered.

The operation of the motor 82 is under the I control of a pair ofelectromagnetic reversmg switches 92 and 93 which are adapted to causethe operation of the motor by extending a connection thereto from theeXciter bus 52 by way of the conductors 95. The

I motor 82 is operated in one direction when the relay 92 is energizedand it is operated in the opposite direction when the relay 93 isenergized, the speed of operation being determined by the setting of thevariable rheo- Stat 97.

The rheostat 42 for varying the induceddraft is controlled in a mannersubstantially identical to the control of the rheostat 41. For thispurpose there is provided a movable me mber 100 driven by either oneorboth of a pair of motors 101 and 102 through a differential 103 underthe control of relays 106 and 107 for the motor 101 and 108 and 109 forthe motor 102. The motor 101 is controlled in the same manner as is themotor 81 and the motor 102 is controlled in the same manner as the motor82. It isto be noted that the motors 81 and 101 are supplied withpotential from the constant potenw tial bus 54 whereas the motors 82 and102 are supplied with potential from the bus 52, the

voltage of which is determined by the adj ustment of the variablerheostat that connects thebus 52 with the bus 54.

An explanation will now be given of the manner of actuating the relays50 and 51 for controlling the coal feed motors, the relays 92 and 93 forcontrolling the forced draft motors, and the relays 108 and 109 forcontrolling the induced draft motors. All of these relays are under thecontrol of the master controller 66. Assume that the steam pressure hasgone down below normal with the result that the master controller 66,under tlie'action of the master steam pressure gauge brings about theapplication of negative po tential to the increase conductor 68. Theapplication of negative battery potential to the conductor 68, whichconductor is connected to the conductor by way of the switch 72 (Figure25), results in a completion of the circuit for the winding of therelays 50, 92,

. and 108 for operating the pilot motors 45, 82,

and 102m a direction to bring about an increase in the speed ofoperation of the respective motors controlled thereby. The circuit forthe relay 50 extends from the negative side of the battery, through theconductor 70, through the conductor 115 to the winding of the relay 50,thence by way of the conductor 116 to the positive side of the batteryby way of the bus 60. The rela s 92 and 108 are likewise connecteddirectly across the conductor 70, which now has negative batterypotential applied thereto, at the positive battery bus 60. All three ofthese relays operate and at their front contacts establish a circuit forthe pilot motors 45, 82 and 102, said motors being supplied withpotential from the exciter bus 52. The relative speeds of the threepilot motors will be determined by the particular settings of theindividual pilot motor resistances 48, 97 and 120. The speeds of allthree or" these motors may be simultaneously varied by varying theresistance 55, a variation of which will alter the speeds of the threemotors while maintaining their relative speeds substantially the same aspreviously. The motor 45 will vary the resistance 40 to increase thespeed of operation of the coal feed motors and,

assuming that the motors 81 and 101 are not operating at this time, themotors 82 and 102 will likewise efl'ect the resistors 41 and 42 toincrease the forced draft andthe induced draft. The apparatus may be socalibrated portion to the speed of the motors 82 and 102. Reverseoperation of the motors 45, 82, and 102 is brought about by theenergization of the relays 51, 93, and 109, respectively, said relaysbeing energized when negative battery potential is applied to conductor71 instead of to the conductor 70. This negative potential is applied tothe conductor 71 through the master controller 66 by way of the decreaseconductor 69 in the event that the boiler pressure rises above apredetermined normal amount.

From the above description it may be seen that the coal feed motors12-'12 and 12'12, the forced draft motors a3 and 23, and the induceddraft motors 32 and 32, all shown in Figure 1, are under thesimultaneous control of the master pressure gauge 66 by Way of thecontrol conductors 70 and 71, the rela tive rate of operation of therespective roups of motors being under individual control of theresistors 48, 97, and 120. It is also apparent from the description thusfar given that these motors may all be simultaneously controlled bythe'hand operated switch 142 upon the proper setting of the transferswitch 141, the rate of increase or decrease in the speeds of the motorsbeing again deter mined by'the settings of these last mentionedresistors.

As previously stated, it is necessary to maintain the ratio of theforced draft to the induced draft at a certain predetermined amount inorder to obtain the most efficient utilization of the air used. Aspreviously stated, the furnace pressure is a function of the ratio ofthe forced draft to the induced draft, this pressure going up as theforced draft is increased and going; down as the in duced draft isincreased. I thus so employ the furnace pressure gauge to regulate theforced draft to maintain this ratio constant. Assume for a moment thatthe total quantity of air passing through the furnace per unit of timeis the proper amount required for he rate of fuel comlmstion but thatthe ratio of the forced draft to the induced is mproper. Let us assumethat the forced draft is slightly too high and the induced draft isslightly low. The furnace pressure gauge will therefore tend to slowdown the forced. draft fan to bring this ratio back 50 the normalrequired amount. Upon the first slight decrease in speed of the forceddraft fans there will. be a tendency for the total quantity of air beingblown through the furnace per unit time to decrease. This will ch angethe ratio of the fuel flow to air flow. The fuel flow to air flow ratiometer 31 will therefm'e become effective to increase the induced draftto increase the amount of air flowing through the furnace. This willalso tend to br ng: the ratio of the forced draft to the induced draftback to normal. Therefore both of these features will function at thesame time to maintain not only the ratio of the forced. induced draftbut also the ratio of the fuel flow to air flow. On the other hand,assume a state of affairs when the ratio of the forced draft to theinduced draft is at ts rei'i 'uirod amount but that there is animamicient amount of air supplied for the amount of fuel burned. Thismeans that both the forced draft and the induced draft must he increasedto increase the rate of ir flow. My improved mechanism accomplishes thisresult. The fuel to air ratio being too low, the efficiency meter 31,will be actuated to increase the induced draft. This will change theratio of the forced draft to the induced draft ith the result that thefurnace pressure gauge 33 will be actuated to increase the forced draftat the same time that tie induced draft is being increased therebymaintaining the proper ratio. It is apparent froin the above descriptionthat the furnace pressure gaugn: 33 could be interchanged with thefuelto air ratio gauge 31 without effecting the operation of my system.

An explanation will now be given of the circuits controlled by the fuelto air ratio meter, or efficiency meter 31 for varying the resistance42.. T 1e movable element of this meter is adapted to be connected tothe positive side of the bus 60 by means of a douhle-tln'ow switch 125and. a conductor 1%. ll hen the switch 125 is closed against the. righthand contact as seen in Figure 2, thereby applying the positivepotential to the movable element of the efficiency meter, this movableelement may energize the winding of the relay 106 at its left handcontact or the winding: of the relay 107 at its right hand contact. Itis to be noted that each of the windings has one end thereof connectedto the respective contact controlled by the movable elements of thefliciency meter and that the other ends of the two windings areconnected together and to the negative battery bus 60. The encrgizationof either of the two relays c1 10. will establish a circuit foroperatilu); the motor 101 in one direction or the other, said circuitextending from the motor 101 through an adjustable rheostat 30, throughthe corrc spending front contact of the particular one of the two relayswhich energized, thence by way of the conductors 131 and the closedswitch S9 to the bus 54. The motor 101 will now operate at a speeddetermined by the settine; of the resistance 130 and this regardless ofwhether or not the motor 102, under the control of the master controller60, is or is not operating. The motor .101 actuates one of the elementsof the differential 103 to actuate the member 100 to regulate theresistance 42. Vfhcn the switch is in engagement with its left handcontact it places the ones-gi- Zation of the relays 106 and 10. underthe control of the hand operated switch 135, which upon being depressedplaces positive battery potential upon the conductor connected to thewinding of the relay 107, whereas upon being elevated it places thispotential upon the con ductor that produces the operation of the relay106. This is provided to facilitate the hand adjustment of the rheostat42 under the control of the motor 101.

The fu rnace prcssure gauge 33 controls the energization of the relaysand 87 for controlling the motor 81 in a manner identical to the controlexercised by the eiiiciency meter 31 over the windings of the relays 106and 107. When the manually operable transfer switch closes itsright handcontact then the furnace pressure gauge and the efficiency meter 31 areboth effective to automatically control the respective pilot motors 81and 101, respectively. hen the manually operable transfer switch 125 isoperated to close its left hand contact control is taken away from bothof these meters. Under such conditions the relays 106 01-107 may beenergized by the push button 135, as previously described, whereas;

the relays 86 and 87 may be controlled by the manually operable pushbutton 140. lVhen this push button is depressed it establishes'a circuitfor the winding of the relay 87, whereas when this push button is raisedit' establishes a circuit for the winding of the relay 86. Thus, byoperating the manual switch 125 to close its left hand contact, theindividual pilot motors 81 and 101 maybe selectively controlled by meansof the respective push buttons 1'40 and In Figure '2?) I show, inaddition to the master controller, in diagrammatic form, controlcircuits for two additional boilers. Each of these circuits is identicalto that shown in Figure 2a and therefore the major portion of thecircuits has been omitted. It is sufficient to say that the commonincrease and decrease control conductors 68c and 690, which extend tothe control circuit for boiler No. 1, as shown in Figure 2a andpreviously described, also extend to the control circuits for each ofthe other boilers. The parts of the control system for furnace No. 2have been given the same reference numerals as corresponding parts ofthe control system for furnace No. 1, the subscript 2 being added, thesame arrangement being followed for furnace No. 3, the subscript 3 beingadded.

From the description thus far given it is apparent that the manuallyoperable transfer switch 7 2 (Figure '25) takes control away from theautomatic action of the master con-. troller 66. and transfers it to thehand switch 7 5 for simultaneously regulating all of the control motorsof all of the furnaces; the manually operable transfer switches 141 areeach effective for transferring the control of the motors that regulateany one furnace, from the master controller to the hand switch 142,which can then simultaneously control all of the regulating motors forthe one parover a wide range.

ticular furnace involved. The manually operable transfer switch 125 ofeach furnace transfers the control ofthe forced draft and the induceddraft for that furnace from the efiiciency controls 31 and 83 to theindividual hand switches and 135 for separately controlling the forceddraft and the induced draft.

By varying the resistance 55 of the controls of furnace 1, the rate ofresponse of all of the pilot motors of this furnace under the control ofthe master controller 66 may be varied. In a like manner by varying theresistances 55 and 55 the rate of response of all of the pilot motors offurnace No. 2 and furnace No. 3 under the control of the mastercontroller may be varied. The resistances associated with each of thepilot motors, such as the resistances 48, 90, 97, 130, and 120, ofFigure 2a, are provided for varying the relative rates of response ofthe pilot motors of any one furnace.

The system as disclosed in Fig. 2 offers an unusual degree ofreliability or continuity of service. Whereas in other systems thevarious elements of combustion depend for their controlon one actuatingunit, such as a single pilot motor actuating a rheostat or damper, thissystem provides for two pilot motors actuating each of the draftcontrollers. In case of failure of either pilot motor on either of thedraft controllers, the other motor on that controller will maintainsubstantially correct operation. For example, should the pilot motor 102furnishing the master steam pressure adjustments to the induced draftcontroller 42 or either or both of its reversing switches 108, 109 failto operate, the induced draft controller will follow changes in thedemand on the boiler, under control of the efficiency responsivecontroller 31, which will operate through the other pilot motor 101 tomaintain the correct proportion of fuel to air supply.- Hence, anychange in boiler demand will change the rate of fuel feed which willautomatically call for a readjustment in induced draft to maintain thecorrect fuel/air ratio. Likewise, if the pilot motor 101 or its control,should fail to operate, the other pilot motor 102, responsive to themaster controller, will continue to adjust the induced draft controllerresponsive to the load on theboiler, and will thereby maintainapproximately a correct fuel/air balance with an occasional handcorrection if the boiler demand should vary In the same manner either ofthe two pilot motors 81, 82 on the forced draft controller 41 willmaintain an the boiler would then merely continue to all "' resistance41.

operate at a. constant firing rate and other boilers would carry theswingsin demand.

Reference may now behad more particularly to Figures 8 and 4 wherein Ishow the arrangement of-the differential such 83 and the pilot motors 81and 82 for operating the same. The arrangement of the differential 103and of the motors 101 and 102 forregulating theinduced draft isidentical to that for reguiuti the forced draft. The pilot motor 81drives a worm which in "turn engages and drives a worm wheel- 161. Theworm and worm wheel are mounted in a gear ho sing 162. The worm wheel161 mount ed upon and drives a hollow shaft 163 which is journal-ed insuitable bearings at 1G-l16t and extends outsioe of the housing 162. Thedifferential-L: indicated at 83 and one of the driving gears thereof ismounted upon and keyed to the shaft to be driven thereby. Sui ablebearings are provided at for faci. .iting; the turning of the gear-168with reference to: thedifierential-housing 83. T he housing 83constitutes the spider'of the differential will appear-as thisdescription proceeds.

The motor 82 Cll'lI-QS a worm 170 w iich in turn drives a worm wheelll'l within a gear housing 172. The gear 1?]. is mounted. upon and keyedto a shaft 173 which is jouyrna-led in suitable bearings lT l-dT l inthe housing. This shaft ext casing 83, being in a ;nment with t 1653. Agear 176 islreyed to and a the shaft 173, suitable hearings boronlocatedz "178 to facilitate turning of this gear with -'efcrence to tne gearhousing. A differential e shaft 81 so as to hefreely rotatable withrespect ucreto and 18111 mesh with the gears 166 and g in oppositedirections and at the no speed. the ditfcreutialshaft 181 will. remainstationary. If the gears 186 andli'd spindle rota is a shaft 183 thatextends through the hollow shaft- 163. This'shaft 183 may be arranged toopcratethe driven element 80 (Figurel2a) that controls the in Figure llhave shown a bevel gear mounted upon the shaft183, said ar mesh innwith as si1'1'1il:u'- ;'car-186 that is arranged to drive an arm of apotention'ieter resistance 187. The arm is indicated at 188 and is movedbacl-twards or IOYWQI'd hy mea. s of a worm 189 driven by the gear 186,said mo ing over the contacts'lQO- and 191 for varying; the resistance.

' 176 is rotated by the motor 82 I) under the control of the master thenends :into the ditferentialar is mountedupon a differential shaftboth-gears ltidand 176 the driven shaft 183 will operate at a certainspec l. If, in addition, the gear 186 is also being driven in the samedirection then the shaft 183 will operate twice as fast, permitting thedraft change under the control of the efficiency meter to actually catchup with the main control.

While I have herein shown the fuel to air ratio as being controlled bythe ei'liciency meter 31, which is the carbon dioxide meter, thiscontrol may be exercised by the efliciency meter 34 which is a meterthat indicates the ratio of the steam flow to air flow. Either of thesetwo meters will give variations which are proportional to the variationsin the ratio of air flow to fuel flow since on the one hand thepercentage of carbon dioxide inthe flue gases is proportionate to thisratio and, insofar the efliciency meter 34 is concerned, the steam flowproportionate to the coal fuel flow.

I prefer to use an arrangement wherein the furnace pressure gauge 33controls the forced draft whereas the efficiency meter which gives thefuel flow to air flow ratio controls the induced oraft. This may,however, be reversed without departing from the spirit of my presentinvention since-either of these two meters may be used to control one ofthe drafts and the other meter used to control the other draft. I alsopropose, as an alternative, to regulate the'rate of fuel flow undertheoint controlof the master controller and the fuel flow-air flowefficiency meter 31 or 34. In this last mentioned arrangementtheinduceddraft would therefore not be con trolled by: the ef'n-ciency meter. Sucha control arrangement would. be identical to the control arrangementshown in Figure 2a, different therefrom only in that the coal feederrheostat 40 would be controlled by an arrangementidentical to thatshownfor controlling the induced draft rheostat 4-2, and the control for theinduced draft rlieostat would-be such as is shown for the rheostat l0 inFigure 260. (11', stated in other words, the control circuit would heexactly shown in Figure 2a with the resistance 40 connected to controlthe induced draft, and the resis tance 12 connected to control the coalfeed motors.

In Figure 6 I have shown a difl'erent well known form of controllingrhcostat and a drive therefor from the shaft 183. In this instance asprocket 195 is mounted upon and driven by the shaft 188 and transmitsits motion through a chain drive 196 that drives a gear 197 for turningthe arm 198 of the rheostat 199.

Reference may now be had more particularly to Figure 7 wherein I show a.different arrangement for controlling the resistance such as theresistance 41 or 42 of Figure 2a. In this figure the eXciter bus isindicated at .52, the battery bus at 60, and the increase and decreasefiring control conductors and 71, all of said conductors being connectedin circuit identical to that shown in Figure 2. The increase anddecrease conductors are adapted to havenegative battery potentialapplied to one or the other of the two conductors under the control ofthe master controller such as shown in Figure 27). I provide a pair ofincrease and decrease relays 200 and 201 which correspond in function tothe relays 108 and 109, respectively, or the relays 92 and 93,respectively, of Figure 2. If negative potential is applied to thedecrease conductor 71 then the winding of the decrease relay 201 isenergized, whereas if negative battery potential is applied to theincrease control conductor 70 then the winding of the relay 200 isenergized, the circuit for energizing each of these windings beingobvious. At 203 I show an efficiency meter which may be the furnacepressure meter 33 of Figure 2a, or the fuel to air ratio meter 31 ofFigure 2c. The movable element of this meter is con nected to thepositive side of the battery bus and this movable element is adapted toengage either one of two contacts for estab ing a circuit to the windingof an increase relay 204 or a decrease relay 205.

A pilot motor 213 is adapted to be rotated in either direction by therelays 20st and 205 through a circuit including an adjustable resistance210, and is also adapted to be rotated in either direction by the relay200 and 201 through a circuit including an adjustable resistor 217Assume that the increase relay 200 has operated due to the applicationof negative potential upon the increase conductor 70. A motor circuitnow extends from the positive side of the exciter bus 52, through theconductors 214 and 215 and the back contacts of the open relays 204 and201 to the conductor 216, from whence the positive battery potentialextends through the now closed middle cont-act of the relay 200 to thepilot motor by way of the conductor 218. From the pilot motor thiscircuit extends by way of the conductor 219, through the resistor 217,through the closed left hand contact of the relay 200, to the conductor220, from whence it extends to the negative side of the exciter bus overa path which extends through the closed right hand back contact of therelay 205. The pilotmotor 213 will now operate at a speed determined bythe setting of the rheostat 217 and will vary the resistance 225 toincrease the speed of forced draft motor or of the induced draft motordepending upon which motor circuit it controls.

If battery potential is applied to the decrease conductor 71, the relay201 will be operated to operate the motor 213 in the reverse direction.The circuit forthe pilot motor 213 extends, under these conditions,

as follows: From the positive side of the exciter bus, through theconductor 21 1 and he right hand closed back contact of the relay 20 1to the conductor 216, thence by way of the middle front closed contactof the relay 201 and the resistance 217 to the conductor 219, thence byway of the motor 213 and the conductor 218 to the left hand frontcontact of the relay 201, which extends the circuit to the conductor220. At this point the circuit is completed to the negative side of theexciter bus over two paths, one of which extends through the closedright hand back contact of the relay 205 and the other of which extendsthe closed right hand back contact from the relay 200. From thisdescription it is apparent that the pilot motor 213 is operated in onedirection or the other over the increased and decreased conductors 70and 71, under the control of the master controller 66 (Figure 2b) tobring about an increase or decrease of the resistance 225, which may beconnected to effect the forced draft as is the resistance 41 of Figureor the induced draft as is the resistance 12 of Figure 2a, or the coalfeed as is the resistance 10 of Figure 2a.

The relays 20-1 and 205, under the control of the special control 203are effective to establish connections to produce a rotation of thepilot motor 213 in one direction or the other lepending upon which ofthe relays is energized. In either event the circuit extends through theresistor 210. These circuits are believed to be obvious from thedescription thus far given and need not be repeated at this time.

A description will now be given as to the operation of the system in theevent that bhth of the .a case relays 20-1 and 200 are operatedsimultaneously, or in the event that bbth of the decreased relays 205and 201 are operated simultaneously. First let us assume that theincrease relay 201 is operated when the relay 200 is in its operatedposition. The relay 200 extends positive exciter potential to theconductor 218 and negative exciter potential to the conductor 219 by wayof the rheostat 217. At the sametime negative exciter potential is beingapplied to the conductor 2 9 by way of the resistance 210 and the lefthand now closed contact at the relay 20st. The relay 20st also appliespositive potential to the motor conductor 218. Since negative batterypotential is now being applied to the condrctor 219 by way of theresistors 210 and 217, it is apparent that these two resistors areconnected in parallel and that the net eifect of this is to decrease theeffective resistance between the conductor 21!) and the negative exciterbus. As a result the motor 213will rotate in a direction to increase thespeed the draft fans. this pilot motor operating at a greater speed thanthat which it operates when only one of the lib.

-' under such a condition positive pots.v

' of the motor circuit by the other of these two resistors 210 and 217is included in the circuit. It is thus apparent that under theseconditions the special control 208 produces an additive effect upon themotor 213 over that produced by firing control conductors acting alone.

in a like manncrit both ot the decrease relays 905and 201 are closed atthe same time then positive ei-zciter potential will be applied to theconductor .219 byway of the two ated.

with explanation will now bev given as to what willv happen it the increse relay 2W undcrthe control oft-he special controllin- 203 is operatedat the time that the decrease relay 201 hasbeen closed by the mastercontrollertid. It is to beremeinbered that the motor circuit receivesits negative potei'itial by way of the conductor 220 and its-positivepotentialby way of the conductor 216. However, when both of these relaysare operatei'l no positive potential is applied tothe couductor 216since the'back contact of therelay d and the back contact of the relay201 are botl'i open. It is therefore apparent that iial is not appliedto either side of the motor circuit although the negative potential isapplied to one side of the motor circuit by one of the relays 204;201and to the other side two relays. Since the motor circuit is notcompleted bacl: to the positive exciter bus, the motor does not operate.In a like manner it the decrease relay 205 is operated by the specialcontroller 203 at a time that the increase relay 200 is in its operativeposition then again the motor circuit is not completed since thenegative side oil-the line open at the right hand back contact oi therelay 205 and also at the right hand back contact of the relay 200. Themotor 213, here-fore, does not operate. This is exactly as it should besince it one of these relays tends to control the draft in a manner toincrease the draft whereas the'other relay tends to control the draft ina manner to decrease the same then it is apparent that no change in thedraft should be made. This some action is obtained by the mechanicaldillerential shown in Figure 2a by the subtractive action of themechanical differential arrangement.

Reference may now be had to Figure 8 wherein I show an alternate methodfor controlling the pilot motor 213 of Figure 7. In this embodiment ofmy invention the operation of the motor 213 is controlled by an armpivoted at and adapted to be swung in either direction. The direction ofoperation of the motor depends upon the direction of movement of the arm260 and the speed of operation of the motor depends upon. the extent ofthe movement of this arm. It is elieved that the motor circuits will beapparent from the description thus far given. It is merely necessary tostate that the arm 260 has a conducting port-ion adapted to bridge thecontact conductors EGG-26? or 269 267 andv has another conductingportion 268 insulated from the portion 265 for establishing; a bridging;connection betweenthe inner resistor and the inner circular con tactscg'n'ient. Th. arm 260 is adapted. to be swung in direction by eitherone of two electromagnetic coils 280 and 281, and is adapted to he swungin the otherdirection by either one or both oi? two electromagneticcoils 232 and 9283. The coils 280 and282 are controlled over theincrease anddecrease conductors and T1, respectively, and correspond tothe windings of the relays 200 and 201 of Figure '5. The coils 281 and288 are adapted to be controlled by the movable element of the gauge 203which may correspond to the gauge 33 of Figure Qaor to the. gauge ofthis sank. figure. Adjustable regulatinp; resistan are provided in thecircuits of the respective coils 280 to 283 for regulating the eli'ectsor these coils. Springs 2852S5 a re provided for returning thearm 260 toits neutral position. If one of the two coils on one sideof the arm 26001 one of the cons on the other side of the arm 260 isenzed then thisarm will be swung one direction or other to a certain extent. If both otthe coils on one side of the arm or both of the coils on the other sideof the arm are simultaneously energized then thisarm will swing in thecorresponding direction by a greater amount, thus causing a greaterspeed of operation of the pilot motor 218. It two relay windings on theopposite sides of the arm 2-60 are simultaneously energized then the armwill not be moved in either direction. That this is the desiredoperation is believed to be apparent from the preceding do. iption.

lVhile in Figure 1 have shown a furnace wherein the torced draft and theinduced draft are both produced by variable speed motors, these draftsbeing varied by varying the speed of the motors, the variation in thedraft may be produced in different manners. For instance, the forceddraft fans and the induced draft fans may be driven by constant speedmotors and the ellect of the fans may be varied by damper control. Itdamper control of the air flow is used then. the movable element ofFigure 2a and the movable element of this same figure, control thedampers for the forced draft and the induced draft, respectively. Thiscontrol may be exercised through a direct mechanical connection orthrough a pilot motor. If the regulating means shown in Figures 7 or 8is used then the pilot motor 213 may be arranged to control the extentof damper opening.

By means of the system thus far described an adjustment of the firingrate and air flow for each boiler may be accomplished. Now it frequentlyoccurs that it is desirable to fire one of the boilers at a reduced rateas compared with another. If the total load is increased, it will beapparent that one of the boilers may be fired at an increased rate totake care of the increased load, or all of the boilers may be fired at aproportionately increased rate to carry the increased load whilemaintaining the proportionate loading between the boilers. In order tomaintain a proportionate loading upon all of the boilers at all times,it is necessary, or at least desirable, to provide some sort ofregulating means for maintaining the proportionate loading on therespective boilers in the event that a variation in the relationship ofthe loads carried by the respective boilers should occur.

I consider that the most effective way to handle the situation is thatso long as changes in load are relatively minor as compared with thetotal load capacity, such changes and demand should be met by aproportionate change in the rate of firing of all of the boilersoperating together. For the purpose of proportioning the load, oneboiler is assumed to be a master boiler and the load of the others isadjusted relative to it. Then, for variations in load, the entire groupis fired more or less to meet the variations in demand.

In order to maintain the highest degree of efiiciency of the respectiveboilers, it is desirable that each boilershould remain under the controlof its individual special efiiciency control at all times, even thoughregulation may be taking place for proportioning the loads on therespective boilers.

In Figure 9 I show an arrangement for maintaining at all times, thedesired proportionate loading of the respective boilers. The automaticload division maintaining means is adapted to be included in the systemshown in Figure 2a, and I have shown, in Figure 9, as much of the systemof Figure 2a as is deemed to be necessary for an understanding of themanner of connecting the automatic load division maintaining means inthe system shown in Figure 2a. Correspending parts of Figures 9 and 2have been given corresponding reference numerals.

Since the rate of firing is that of the rate of coal feeding, and therate of coal feeding in my system is d pendent upon the potentialsimpressed upon the armature circuits of the coal feeder motors, it ispossible to maintain any desired ratio of feeding, and that can be doneby maintaining the corresponding ratio of voltages upon the coal feedermotor armature circuits.

In Figure 9 I have shown, in diagrammatic form, the coal feed motorcircuit arrangement. This includes a motor generator set 300 comprisinga constant speed alternating current motor 301 driving a direct currentgenerator 302 having a field 303 under the control of the resistance 40,which resistance is varied as shown in Figure 2. This generator suppliesvariable potential for operating the coal feed motors 12 at the desiredspeed. The speed of the motors 12, hence the rate of firing of theboiler 1, will be determined by the voltage of the generator 302, and bycomparing this voltage with the Voltage of similar generators of thedifferent boilers a comparison of the firing rates of the respectiveboilers may be had. For this purpose a set of conductors 308 extend thepotential of the generator 302 to a set of conductors 310. The voltageon the conductors 310 controls suitable instrumentalities, as will nowbe explained, for automatically maintaining the relation of firing rateof'one boiler with respect to the other boilers.

In order to automatically maintain the relation of the firing rate ofone boiler with respect to the other boilers I provide each boilercontrol system with a differential relay 315. Each of these differentialrelays comprises a pair of coils, 316 and 317, the coil 316 beingconnected to the coal feeder bus 310 of boiler No. 1 so as to beenergized in proportion to the voltage on said bus, which is thereforein proportion to the rate of firing of boiler No. 1. In series with thecoil 316 I provide an adjusting rheostat 318 for regulatin the currentflow through this coil, for the purpose of maintaining a balancedrelation between the voltage of the bus 310 and that of the load balancebus 320 to which the coal feeder potential bus of any one of the boilersmay be connected. Assume that boiler No. 2 is connected to the loadbalance bus 320, as indicated by the plug switch 321, and assume furtherthat the potential upon the coal feeder potential bus 308 is the fullpotential corresponding to the normal firing rate. The rheostat 318which is connected in series with the winding 316 is so adjusted thatthe predetermined lower voltage on the bus 310, acting through thevoltage differential relay winding 316 will inst balance the normalvoltage applied to the winding 317 acting through a series resistance323, the less resistance 318 connected in circuit the lower will be thefiring rate of the corresponding boiler U0. 1.

The coils 316 and 317 operate upon a bala nce member having amovableContact 324 and adapted to engage a contact upon its right hand side ora contact upon its left hand side to increase or decrease the rate offiring of the boiler. These contacts control the circuits of an increasecut-in relay 325 and a decrease cut-in relay 326. It is to be noted thatthe circuit from the common increase and deer use firing controlconductors 69c and (390 extend through back contacts on the lays 325 and326 to the contacts of the switcl 141. la the circuit shown in Figure 2athe conductors {38c and (390 lead directly to the contacts of the s(itch 14-1 inst aid of through contacts of relays such as the cut-inrelays 325326. lt is thus apparent from the circuit shown in Figure 9that the energization of either of the two cut-in relays 325 or 326 willlute 'rupt the control by mrcr 1r coin troller over the particularboiler 'nv led and will substitute therefor the co itrol by the differenfiial relay which controls the relays S and Upon energization ofthe relay 325, negative potential is applied four the negative side ofthe conductors by way of the conductor and the lower ffO'ilt conti ct ofthe relay to tie conductor which entends the potential by way of theswitch l l; to the increase firing control conductor 70. In a likemanner upon the energination of the relay the negative potential is applied by way of the lower front contacts of this relay to the conductor330 and thence by way of the switch lil to the decrease tiring controlconductor 71.

The windings 31? of each of the differential relays 3153 are connectedin pa allel by way of the set o conductors 320. lie set of con ductorsis adapted to have applied there to volte' e which is c'c i to thevoltage apl. plied to g motors of any one of the the lir'-..

nined by the settmg of the which may be located plug switch 3n as ormayl c shown in ll loca ed to est-ablish connec ween the contacts 341-0or the con acts fill. As shown, boiler No. 2 constitutes the n'iastcrboile f and the load division is made with refe ence to the load on thisboiler, The peter al aoplied to each of the right hand windings of the{i rential relays 315 of the res )ective boiler. 'oportionate to thevoltage applied to ti 9 motors of whereas the iotc applied to idwinnings of eacl "he relays rticaiale to the iotor of boiler No. l,

relay through the case trol wires of the particular boiler and adjuststhe rate of firing accordingly. As soon as this regulating adjustmenthas been made, the voltage differential relay tends to balance and theoperation proceeds in the proper relation, The control exercised overthe conduc- TO and 71, of Figure 9, is obtained through apparatus andcircuits such as Slit) 'n in Figure 2. It is to be noted that during thetime that the firing of one the boilers is ng adjusted by the action ofthe diferenl ay 315, the individual controls 31 and of Figure 2 stillretain control and main- 1 ti proper fuel to air ratio and forced liftto induce draft ratio of the boiler being gall ted. its a result of thissimultaneous action, the tendency to hunt is materially decreased, ifnot entirely eliminated.

in compliance with the requirements of the "nt statues I have hereinshown and ded a preferred embodiment of my invenon and the method ofoperation of the same. is, however, to be understood that I am notimitcd to the precise details herein shown, he same being merelyillustrative. lVhat I i'der new and desire to secure by Letters .r turnsis:

1. ln combination, a furnace, means for producing a draft in thefurnace, means controlled responsive to the occurrence of an ink a... an

a continuous motion tending to bring about a rrespon'din-g change in thedraft to correct occurrence of an increase or a decrease in the heatdemand on the furnace from a normal amount for prodi cing a continuousmotion tending to bring about a corresponding change in the draft, meansactuated in accordance with the instantaneous extent of the two motionsfor effecting the change in tl e draft, and means for adjusting therelative extents of the two motions.

2. In combination, a furnace, a boiler heated thereliiy, means forproducing a draft in the furnace, switching means controlled responsiveto the occurrence of an increase or a decrease of the furnace pressurefrom a predetermined normal separate switching, means responsive to theoccurrence of an increase or a decrease in the boiler pressure from anormal iount, dilferential means actuated in accordance with theinstantaneous actuation of the two switching means for elfecting achange in the draft and means for adjusting the relative actuation ofthe two switching means.

In combination, a furnace, means for producing a forced draft and aninduced draft in the furnace, means controlled r sponsive to theoccurrence of an increase or a decrease of the heat demand on thefurnace from a predetermined normal for producing a continuing motiontending to bring about a cort re furnace pressure, means respon 'ive tothe

